Such abberations have in the past been corrected by manual adjustment of the cathode ray tube analog drive circuitry. British Pat. No. 1,517,119 proposed that aberrations be corrected dynamically by reading correction signals from a digital store as the beam is being scanned across the screen. The correction signals are, however, directly representative of the corrections to be applied and this implementation is unduly expensive of storage space. Copending application Ser. No. 214,145 filed Dec. 8, 1980 proposes that the correction signals be derived from stored parameters and describes and claims analog circuitry to achieve this end. Although this latter approach is a highly effective means for achieving correction, the reducing cost of digital circuitry makes the digital rather than the analog approach an interesting alternative, especially if the digital circuitry can be kept simple enough to occupy a single chip.